The structure of a System Architecture Evolution (SAE) system is shown in FIG. 1. The structure of the conventional SAE system will be described briefly with reference to FIG. 1 hereinafter.
User Equipment (UE) 101 is a terminal device adapted to transmit and receive data.
An EUTRAN 102 is a radio access network in the SAE system. The EUTRAN 102 includes an eNB, is adapted to provide the UE with an interface for accessing a radio network, and is connected with a Mobile Management Entity (MME) 103 and a user plane entity, i.e. Serving Gateway (SGW) 104, via S1 interfaces respectively.
The MME 103 is adapted to manage mobile contexts and session contexts of the UE, and store security-relevant information of users.
The SGW 104 is mainly adapted to provide a function of a user plane.
A S1-MME interface is adapted to establish a radio access bearer for the UE and forward a message transmitted by the UE to the MME 103 via the radio access network.
Functions provided by the MME 103 and the SGW 104 together are similar to functions of a Serving GPRS Support Node (SGSN) 108. The MME 103 and the SGW 104 may be located in one physical entity.
A Packet Data Network Gateway (PGW) 105 is adapted to perform functions such as charging and legal monitoring. The SGW 104 and the PGW 105 may be located in one physical entity.
A Policy and Charging Rule Function entity (PCRF) 106 is adapted to provide a Quality of Service (QoS) policy and a charging rule.
The SGSN 108 is a network node device in the UMTS to provide routing for data transmission. The conventional SGSN finds a corresponding Gateway GPRS Support Node (GGSN) according to Access Point Name.
A Home Subscriber Server (HSS) 109 is a home subsystem of the UE, and is adapted to store subscriber information, including: a current location of the UE, an address of a serving node, security-relevant information of a subscriber and Packet Data Protocol (PDP) contexts activated by the UE, etc.
Along with an increase in the data rate of UE services, the operator has new requirements for the conventional SAE system: proposing that a PDN connection access point of the UE can be closer to the radio access network when the UE accesses a particular service. If a network can support this capability, costs of a transport network will be effectively reduced and better service experience of the high data rate can be provided. In the conventional recommendation, this capability is named Selected IP Traffic Offload (SIPTO). The SIPTO may be applied to networks supporting the eNB and networks supporting Home NodeB (HNB).
In 3GPP, it is proposed that a network needs to support capabilities of SIPTO and Local IP Access (LIPA). The SIPTO includes two situations:
1) The UE accesses a service of the Internet or other outer networks through a Home enhanced NodeB (HeNB)/Home NodeB (HNB), and the network needs to select a user plane node adjacent to the access network or a user plane node inside the access network.
2) The UE accesses a service of the Internet or other outer networks through the eNB, and the network needs to select a user plane node adjacent to the access network or a user plane node inside the access network.
The LIPA means that the UE access a home network through the HeNB/HNB. When performing the LIPA, the network selects a user plane node inside a HeNB/HNB access network for the UE.
In order to support this capability, the network may offload a particular IP traffic which the UE accesses. Therefore, it is required to select or reselect an appropriate user plane network device or gateway (called by a joint name of user plane node hereinafter). For example, with respect to a LTE network, it may be related to selecting or reselecting a SGW and a PGW. With respect to a 3G network, it may be related to selecting or reselecting a GGSN and a GGSN. As shown in FIG. 2, the connection indicated by the dashdotted line includes the SGW and the PGW which are selected for the UE before the SIPTO is performed, the connection indicated by the dashed line includes the SGW and the PGW which are selected for the UE after the SIPTO is performed and which are closer to the access network.